This invention relates to improvement in thread-forming screws, more particularly to a screw in which the end pressure required for initiating thread-forming action in a workpiece is materially reduced without the necessity of forming the screw of an impractical length.
It is known that in a thread-forming screw the use of a steep entry or point angle tends to resist the pickup or starting of the thread-forming action of the screw in the workpiece hole. Therefore, in order to effect thread-forming action it is necessary to apply substantial end pressure to the screw, viz. enough end pressure is required to overcome the resistance of the thread to entry into the workpiece hole.
Recently the gimlet point thread-forming screw has come into use as a machine screw thread for various utilizations in metal wherein the point of screw serves to locate the workpiece hole. In these kinds of screws, however, the starting end pressures are necessarily somewhat high. It is, of course, possible to reduce the entry angle by providing a full length taper which is very gradual. However, a full length taper point of this type would consume too many threads and would thus make the screw length excessive and impractical.